Design and Experimental Analysis of a Medium-Frequency Transformer for Solid-State Transformer Applications

Leibl, Michael; Ortiz, Gabriel; Kolar, Johann W.

doi:10.1109/jestpe.2016.2623679

Cited by 231 publications

(108 citation statements)

References 22 publications

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“…The most common methods are listed below: and the losses due to proximity effects (internal and external) are modeled with a low-frequency asymptotic approximation. The packing pattern is only modeled with the fill factor [2], [6], [10].…”

Section: Perfect Twistingmentioning

confidence: 99%

“…Over the years, different calculation methods have been proposed for the calculation of the losses, which rely on analytical and/or numerical calculations [6]- [11]. However, it is found that the measured losses are often larger than the values computed with the aforementioned methods [1], [2], [12]. Different effects can explain such deviations:…”

Section: Introductionmentioning

confidence: 99%

“…Moreover, terminations can add an impedance mismatch between the strands which leads to undesired circulating currents [2], [12], [14].…”

Section: Introductionmentioning

confidence: 99%

“…In particular, commercially available HF litz wires are frequently found to be subject to imperfect twisting [2]. Therefore, this paper analyzes the impact of the twisting scheme on the losses, which, to the knowledge of the authors, has not been studied in details in the literature.…”

Section: Introductionmentioning

confidence: 99%

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Litz wire losses: Effects of twisting imperfections

Guillod

Huber

Krismer

et al. 2017

2017 IEEE 18th Workshop on Control and Modeling for Power Electronics (COMPEL)

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Abstract-High-Frequency (HF) litz wires are extensively used for the windings of Medium-Frequency (MF) magnetic components in order to reduce the impact of eddy current losses that originate from skin and proximity effects. Literature documents different methods to calculate eddy current losses in HF litz wires, however, most of the computation methods rely on perfect twisting of the strands, which is often not present in practice. This paper analyzes the implications of imperfect twisting on the current distribution among the different strands of HF litz wires and the corresponding losses by means of a fast 2.5D PEEC (Partial Element Equivalent Circuit) method. The effects of different types of twisting imperfections (at the bundle-, subbundle-, or strand-level) are examined. It is found that imperfect twisting can lead to increased losses (more than 100 %). However, perfect twisting of the strands, which is difficult to achieve, is often not required, i.e. suboptimal twisting is sufficient. Analytical expressions are given for distinguishing between critical and uncritical imperfections. The experimental results, conducted with a 7.5 kHz / 65 kW transformer, reveal a reduction of the error on the predicted losses from 52 % (ideal HF litz wire model) to 8 % (presented model) and, thus, confirm the accuracy improvement achieved with the proposed approach.

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Section: Perfect Twistingmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

“…Moreover, terminations can add an impedance mismatch between the strands which leads to undesired circulating currents [2], [12], [14].…”

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Litz wire losses: Effects of twisting imperfections

Guillod

Huber

Krismer

et al. 2017

2017 IEEE 18th Workshop on Control and Modeling for Power Electronics (COMPEL)

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“…Note that no detailed isolation coordination such as in [2] is carried out, because the focus lies on evaluation of the IFE topology, not on the transformer design, which is covered by corresponding literature [2], [24]- [27].…”

Section: B Key Components Of the Realized Prototypementioning

confidence: 99%

Analysis and Cell-Level Experimental Verification of a 25 kW All-SiC Isolated Front End 6.6 kV/400 V AC-DC Solid-State Transformer

et al. 2017

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Abstract-Solid-state transformers (SSTs) could serve as interfaces between a medium-voltage (MV) AC grid and a low-voltage (LV) DC load or source, i. e., could be employed in applications with power supply character such as traction auxiliary supplies or rack-level power supplies in future datacenters. For handling the high input-side AC voltage and output side current, SSTs are typically realized as input-series output-parallel (ISOP) arrangements of multiple converter cells, whereby each cell comprises a medium-frequency isolation stage. This paper presents such a multi-cell 25 kW all-SiC MVAC-LVDC SST (6.6 kV AC to 400 V DC) based on the isolated front end (IFE) approach, which is an interesting alternative to the isolated back end (IBE) configuration mainly discussed in literature so far. The IFE concept is briefly explained, the main component stresses are derived, and a converter cell prototype is designed and tested. The 5 kW prototype cell features a power density of 1.5 kW/l (24.6 W/in3) and a measured peak efficiency of 97.5%. This is significantly higher than previously published data for IFEbased SSTs, and in the same range as what has been reported recently for industrial IBE-based SSTs. Thus, this paper confirms that the IFE approach can be a feasible and interesting alternative for realizing MVAC-LVDC SST systems with low complexity.

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Ronanki

2022

Transportation Electrification

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Design and Experimental Analysis of a Medium-Frequency Transformer for Solid-State Transformer Applications

Cited by 231 publications

References 22 publications

Litz wire losses: Effects of twisting imperfections

Litz wire losses: Effects of twisting imperfections

Analysis and Cell-Level Experimental Verification of a 25 kW All-SiC Isolated Front End 6.6 kV/400 V AC-DC Solid-State Transformer

Overview of Rolling Stock

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